Given their way the US would arm every soldier with a nuclear rifle if they could
Many years ago at reddit - I saw that somebody had made a nuke “Davy Crockett” joke. For about 10 seconds I had this dialog with myself in my head “That can’t be real. But could it? But it can’t. Davy Crockett? How can that be real. I’m the world’s dumbest man - I’ll google.” I still can’t believe they named it Davy Crockett.
You could apparently theoretically make an nuclear hand grenade using californium, but it’s completely impractical since you would need 2,7 kg of it, while the yearly production is below 1 g and it have halflife of 2,6 year.
And there’s a small caveat that a man throwing such a grenade would be inevitably caught in the blast.